The present invention relates generally to ultrasonic inspection systems, and more particularly to an ultrasonic inspection apparatus including an acoustic mirror and to methods for ultrasonic inspection of parts having curved surfaces.
Ultrasonic inspection may be used to detect defects inside an object when the defects are located beneath the exterior surface. When an ultrasonic inspection is performed, a transducer is calibrated on a block having a planar entry surface (i.e., flat-top block) made from the same material as that being inspected, and containing flat bottomed holes of known diameter and known depth from the surface. A set of inspection parameters, such as gain, operating frequency, and water-path, are set and calibrated to the flat-top block. The inspection parameters are used to inspect production hardware.
Conventionally, curved surface parts with surface curvature larger than about 38 cm radius are inspected like parts having planar surfaces. For radii less than 38 cm, typically the operator will increase the gain (energy level) in an effort to compensate for losses due to the curved entry surface. Increasing the gain, however, also increases both the system noise (electronic noise) and the material noise. Thus, some production parts become uninspectable because of “high noise.” Because the ultrasound beams can be de-focused or over-focused by curved entry surfaces, the problem is escalated during subsurface inspection.
U.S. Pat. No. 6,253,619 discloses an ultrasonic inspection system that utilizes a transducer to emit ultrasonic radiation that is shaped and reflected by an adjustable acoustic mirror. U.S. Pat. No. 6,237,419 discloses an aspherical curved element transducer to inspect a part with a curved entry surface. These disclosed systems and methods do not provide desired outcomes for subsurface inspection of parts having curved entry surfaces.
Improving ultrasonic inspection capabilities through curved surfaces is desired in the art. Scientists and engineers continue to seek improved ultrasonic inspection systems and methods for inspection through curved surfaces that imitate the inspection sensitivities of inspection through a planar entry surface.